The
graph shows two important things: It shows the average temperature at
the overwintering sites in Mexico during each month of the year and the
graph shows when the monarchs arrive and when they leave.

During
the months that the monarchs are in Mexico, overnight low temperatures
hover just above freezing. The night-time temperatures are similar to
those in your refrigerator!

The
forest shelters monarchs by keeping a very delicate balance:

The
forest protects the monarchs from extreme cold. If the butterflies get
too cold, they will freeze to death

The
forest protects the monarchs from getting too warm. If the
butterflies get too warm, they will burn their stored fat too quickly.

With regard
to temperature, "The really critical time for the monarchs is January
and early February when it's the coldest time of the season," says
Dr. Brower. "We know temperatures below -8 degrees C will kill
about 50% of the monarchs. If the butterflies are WET, it will kill
close to 80-90% of the monarchs."

Thinking
More About the Graph

To get
comfortable with the concept of "average low temperature,"
record your own low temperature each night for a few days, then calculate
the average.

How
many degrees did your temperatures fluctuate above and below the
average?

Dr.
Brower says "-8 degrees C will kill about 50% of the monarchs."
Look back at the graph. Draw your temperature fluctations beside
the values shown. Did your average temperatures fluctate enough
to be of concern?

Write
the temperature for each month on the graph in degrees Fahrenheit. Then
edit the scale to Fahrenheit. (Here is a conversion
scale to help you.)

Remember This graph shows the average temperatures.
This means the daily low temperatures can fluctuate
above and below the temperatures shown.